Non-invasive electronic apparatus for measuring blood pressure

ABSTRACT

A 3-way solenoid valve ( 20 ) is arranged between a cuff ( 10 ) and a first pressure sensor ( 30 ), wherein the common port of the 3-way solenoid valve ( 20 ) is connected with the first pressure sensor ( 30 ), the normally open port thereof connected with the cuff ( 10 ), and the normally closed port thereof connected with the air atmosphere during zeroing process. Moreover, an independent timing circuit ( 45 ) is provided additionally. In the measurement method of the present invention, the zeroing is performed with the help of the 3-way solenoid valve ( 20 ). Once a state of overtime or overpressure occurs, an air pump ( 50 ) is immediately closed, and a quick-deflation solenoid valve ( 60 ) is opened so that the pressure in the cuff ( 10 ) is released to ensure safe application.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/312,815, filed Dec. 20, 2005, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus for measuringblood-pressure and pulse rate for diagnosis, and particularly to anon-invasive electronic method and apparatus for measuring bloodpressure which can correctly calibrate zero pressure, and process thedata acquired during electronic blood pressure measurement by analgorithm of fitting for recovering a trend envelope of oscillating PW(i.e. pulse wave).

BACKGROUND OF THE ART

The non-invasive methods for measuring blood pressure in prior artemploy the oscillometric method on the basis of cuff PW. Thenon-invasive method for measuring the blood pressure of human bodymainly comprises an auscultatory method using Korotkoff sound (simplyreferred as Korotkoff sound method) and proportional coefficient methodusing cuff oscillating wave (simply referred as oscillometric method).

Korotkoff Sound method means that, the experienced medical personnel usea stethoscope, a mercury pressure gauge, a cuff and aninflation/deflation bag, wind the cuff around a proper position of anupper arm of the living body on examination, press the stethoscope closeto the humeral artery, inflate the cuff via the inflation/deflation bagto increase the pressure until the block of the blood flow, and thenrelease the cuff pressure step by step via the inflation/deflation bagto recover the blood flow in the arm. During the deflation process, theexperienced medical personnel can hear the Korotkoff sound through thestethoscope and mercury pressure gauge, which changes from small tolarge and then from large to small due to the blood flow pulse in theartery of the arm during the deflation process, and thereby candetermine the systolic pressure and diastolic pressure. While thesoftware in the system performs the inflation and deflation controlmentioned above, it also identifies the cuff pressure and PW within thecuff detected in respective steps during the deflation process with thecharacteristic wave, and recovers the trend envelope curve of the cuffoscillating wave on the basis of such characteristic PW. The recovermethods of different facilities may differ from each other. Since therecover method has a direct effect on the formation of the envelopecurve, it will to a large extent determine the accuracy of measuring theblood pressure of human body. The method widely used nowadays refers torecovery of the PW amplitude value between steps by linear interpolationmethod, elimination of abnormal fluctuations by multi-point movingaverage method, and thereby acquisition of envelope curve of the PWamplitude by linear fitting.

The method for measuring the blood pressure based on oscillometricmethod is currently applied to most of the electronic apparatus formeasuring blood pressure. The basic process of this oscillometric methodis quite similar to that of auscultatory method, that is, increasing thecuff pressure by inflation to block the blood flow in the arm, reducingthe cuff pressure gradually by deflation to recover the blood flow inthe ram, and detecting the static state pressure in the cuff andpressure pulse wave (PPW) due to the pulse of the artery blood. However,the calculation of blood pressure in this measuring apparatus isachieved by the following steps of: detecting the PPW in the cuffgenerated by the change in artery blood pulse of the arm during thedeflation process and the corresponding cuff pressure, wherein a set ofPPW with the amplitude varying from small to large and vice versa and acorresponding cuff pressure varying from large to small can be detected;then, taking the cuff pressure corresponding to the maximum value of thePPW as an average pressure and utilizing the empirical value for theamplitude proportional coefficient of the PPW to estimate the systolicpressure directed to a higher cuff pressure and the diastolic pressuredirected to a lower cuff pressure (in short, the proportionalcoefficient method based on cuff oscillating pulse amplitude). Thesystolic pressure and the diastolic pressure can be obtained bymultiplying the maximum value of the PPW by two coefficients smallerthan 1.

The electronic apparatus for measuring blood pressure generallycomprises the followings: (i) a pressure sensor for detecting cuffpressure and a processing circuit, (ii) a PPW processing circuit basedon the change in the cuff pressure, (iii) an overpressure sensor as wellas an amplification circuit and a protection processing circuit, (iv) acuff, a control deflation valve, an air pump, gas path connected to thepressure sensor, and an inflation/deflation control section, (v) A/Dconverter and a single chip system, and (vi) power supply portion.During the measurement process, the detection of PPW and the cuffpressure can be performed during the deflation stage following inflationor during the inflation stage. During the deflation stage, the deflationmay be continuously uniform mode (i.e. uniformly decreasing the pressureby 3-5 mmHg while detecting the PPW at the meantime). Alternatively, thedeflation may also be stepwise (i.e. gradually reducing the cuffpressure by a step of 5-10 mmHg, and detecting the PPW at each pressurestep), in which the magnitude of stepwise reduction of pressure isdetermined by the detected amplitude of the PPW. Continuously uniformdeflation leads to time increase for blood pressure measurement, and itis hard to overcome an influence on the arm movement and the bodyposition change, which would limit its application. However, stepwisedeflation leads to time reduction for blood pressure measurement, andeliminates the disturbance resulting from the arm movement and the bodyposition change, etc., with better anti-disturbance capability.Therefore, stepwise deflation is widely adopted in many blood pressuremeasurement apparatus.

As to the oscillometric method for non-invasive blood pressuremeasurement, the blood pressure measurement should be implemented bycombination of hardware and software, wherein the hardware portions aremainly responsible for i) the amplification of the cuff pressure and thePPW signal, ii) another independent overpressure protection circuit forthe cuff pressure, and iii) digital circuit part. The main drawbacks ofthe hardware portions are set forth as follows:

A). the detection of the cuff pressure requires a timed operation ofzeroing, and at present zeroing is automatically performed under thecondition that the cuff is not inflated. However, there exists circuitdrift and it can not be ensured that the static pressure in the cuffduring multiple blood pressure measurement process always drops tonearly “zero”, which will lead to the following results: i) the possiblefailure in zero correction, and ii) the pressure value deviation due tothe offset of zero point even in case of really zeroing. In short, anadverse effect would be exerted on the accuracy in detecting the cuffpressure.

B). In view of safety, two sets of independent timing system arerequired during the blood pressure measurement process to ensure thelimit of measurement time. The blood pressure measurement module in theprior art generally contains a set of timing system itself, and providesan interface to connect with a timing trigger port provided externally.By means of the timing function of the upper computer, not only anotherset of independent timing system can be accomplished, but the safetyrequirement of independent timing can be met as well. However, thisblood pressure module does not perform a complete safety independenttiming and requires the cooperation of the upper computer, which maycause potential danger for the application of such blood pressuremeasurement module.

C). Since the amplitude for the PPW generated in the cuff during theactual deflation process increases from small to large, and thendecreases from large to small after reaching the maximum of amplitude,an asymmetric and non-linear curve of trend envelope is thus formed.Therefore, there are the disadvantages of fitting with linear trend inthat the envelope curve of the PW amplitude can not be correctlyrecovered, and the average pressure, the systolic pressure and thediastolic pressure can be not calculated accurately.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, provided is anon-invasive electronic apparatus for measuring blood pressure, whichcomprises a cuff, a gas pump connected with the cuff, a first pressuresensor connected with the cuff, a second pressure sensor connected withthe cuff for overpressure and overtime protection, a first solenoidvalve unit for deflation, and a first microprocessor, wherein theapparatus further comprises a second solenoid valve which is connectedbetween the cuff and the first pressure sensor.

According to the above-mentioned apparatus of the present invention, thesecond solenoid valve is a 3-way solenoid valve, wherein a common portof the valve is communicated with the first pressure sensor, a normallyopen port thereof is communicated with the cuff during measurementprocess, and a normally closed port thereof is communicated withatmosphere during zeroing process.

According to the above-mentioned apparatus of the present invention, theapparatus further comprises an independent timing circuit with timingfunction, wherein an output terminal of the circuit outputs an overtimesignal to an overpressure and overtime control circuit for overpressureand overtime protection, while an input terminal thereof is connectedwith the first microprocessor for actuating the independent timingcircuit.

According to the above-mentioned apparatus of the present invention, theindependent timing circuit includes a second microprocessor having atiming and triggering function by software, wherein the secondmicroprocessor has two I/O pins connected with two I/O pins of the firstmicroprocessor, for receiving a time delay start instruction and a timedelay stop instruction and an adult/infant setting instruction from thefirst microprocessor; and the second microprocessor further has anotherpin for outputting an overtime signal to the overpressure and overtimecontrol circuit.

According to the above-mentioned apparatus of the present invention, thefirst solenoid valve unit comprises a quick-deflation solenoid valve anda slow-deflation solenoid valve which are connected with the cuff,wherein the quick-deflation solenoid valve is connected with aquick-valve driving circuit and the slow-deflation solenoid valve isconnected with a slow-valve driving circuit, while each of the quickvalve driving circuit and the slow-valve driving circuit is connectedwith the first microprocessor and the overpressure and overtime controlcircuit.

According to the above-mentioned apparatus of the present invention, theapparatus comprises a combined precise amplification circuit including avoltage follower, a preamplifier and an output amplifier which areconnected in series, wherein the combined precise amplification circuithas an input terminal connected with an output terminal of the secondpressure sensor and has an output terminal for outputting anoverpressure signal to an input terminal of the overpressure andovertime control circuit. Moreover, the apparatus may further comprise again control and reference voltage circuit which has an output terminalconnected with an input terminal of the output amplifier. The gaincontrol and reference voltage circuit includes a digital circuit havingthree 2-to-1 bidirectional analog switches which have an output pin Xconnected with an inverting input terminal of the output amplifier, aninput pin X1 connected with a reference voltage V1.25, and a pin X0connected with a reference voltage V2.0.

According to the above-mentioned apparatus of the present invention, theapparatus further comprises a precise amplifier having an input terminalconnected with an output of the first pressure sensor, wherein theprecise amplifier outputs both a pulse signal amplified by a two-stageamplification circuit and a pressure signal to an A/D converter circuit.Moreover, the apparatus may further comprise a gain control andreference voltage circuit which has an output terminal connected withthe two-stage amplification circuit. The two-stage amplification circuitcomprises a preamplifier and a postamplifier which are connected inseries, wherein an output of the preamplifier or the postamplifier isconnected with a first resistor, while a second resistor is in parallelconnected with or not connected with the first resistor via the gaincontrol and reference voltage circuit, which is determined by pins A, Band C of the gain control and reference voltage circuit controlled bySETP and AN_MODE signals from the first microprocessor. Compared withthe circuit design of prior art, the first advantage of the presentinvention is that the connection structure of the gas path is optimized,and the automatic and accurate “zero pressure point” calibration of thecuff pressure is performed without the influence of the residualpressure in the gas path, which improves the accuracy of the measurementof cuff pressure.

The second advantage is that, the independent timing can be performed bymeans of a set of independent timing circuit, which can really implementthe independent timing in the module level and improve the safety duringmeasuring of blood pressure.

The third advantage is that, with the method according to the presentinvention, the envelope curve of the PW amplitude trend can be recoveredaccurately, and the obtained average pressure shows higher degree ofagreement with the real situation in clinic.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the construction principles of themethod and apparatus according to the present invention;

FIG. 2, FIG. 3, and FIG. 4 are flow charts representing the methodsaccording to the present invention;

FIG. 5 is an electric principle diagram of the independent timingcircuit in the apparatus according to the present invention;

FIG. 6A is an electric principle diagram of the sensor and the amplifiercircuit in the apparatus according to the present invention;

FIG. 6B and FIG. 6C are diagrams showing circuits for providingreference voltage VREF and VCC;

FIG. 7 is a schematic graph of trend envelope of the PW amplitudeaccording to the present invention; and

FIG. 8 is a flow chart showing the algorithm of data processing forrecovering the trend envelope of the oscillating pulse wave bynon-linear fitting according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A non-invasive electronic method for measuring blood pressure accordingto the present invention includes the following steps:

i. inflating a cuff communicated with a first pressure sensor which hasbeen zeroed, and then stopping inflation after a cuff pressure reaches apreset value;

ii. deflating the cuff at a preset speed and detecting whether a pulsesignal occurs;

iii. after the pulse signal is detected, processing data with analgorithm for recovering a trend envelope of an oscillating pulse wave,and displaying the measured blood pressure;

during the step i, the first pressure sensor is zeroed in a state ofcommunicating with atmosphere; and

during the step iii, the algorithm for recovering the trend envelope ofthe oscillating pulse wave is a nonlinear fitting algorithm.

In the non-invasive electronic method for measuring blood pressureaccording to the present invention, zeroing operation may be performedperiodically or prior to every measurement process. In this method, asolenoid valve (e.g. 3-way solenoid valve) is used so that the firstpressure sensor is communicated with atmosphere during the zeroingprocess, but communicated with the cuff during the measurement process.

The present invention will hereinafter be further described in detailson the basis of preferred embodiments with reference to the accompanyingdrawings.

As shown in FIG. 1˜4, a non-invasive electronic method for measuringblood pressure, is based on a system comprising a cuff 10, an air pump50, a first pressure sensor 30, a second pressure sensor 40, aquick-deflation solenoid valve 60, a slow-deflation solenoid valve 70, afirst microprocessor (i.e. a primary MCU) 100, a display screen 110, acommunication interface 120, and an upper computer 200. In this system,a 3-way solenoid valve 20 is provided between the cuff 20 and the firstpressure sensor 30. The method includes the following steps:

a. then, when the system is powered to start operation, the solenoidvalve 20 is operated in a state wherein the first pressure sensor 30 iscommunicated with the atmosphere, and then performs zeroing;

b. once the zeroing is done, the solenoid valve 20 is operated in astate wherein the first pressure sensor 30 is communicated with the cuff10; thereby, during the blood pressure measurement process, the air pump50 is operated to increase the pressure in the cuff 10; the uppercomputer 200 receives the data via the communication interface 120 anddisplays the pressure in the cuff 10, or the pressure in the cuff 10 isshown on the display screen 110; and the inflation process is stoppedwhen the pressure in the cuff 10 reaches a pre-determined value;

c. the system adjusts (opens/closes) the quick-deflation solenoid valve60 and slow-deflation solenoid valve 70 to deflate the cuff 10 at apreset rate, and detects whether there is pulse signal;

d. once the pulse signal is detected, the primary MCU 100 processes thedata with the algorithm decided by the firmware through non-linearfitting to recover the trend envelope of the oscillating PW, and thedetected blood pressure value is displayed on the display screen 110 orthe upper computer 200;

e. when the phenomena of overtime or overpressure occurs during themeasurement process procedure, the system immediately closes the airpump 50, and open the quick-deflation solenoid valve 60 to release thepressure in the cuff 10 so as to ensure safe application; meanwhile, thesystem also resets the primary MCU 100;

f. once the measurement process is completed, the quick-deflationsolenoid valve 60 is opened to release the pressure in the cuff 10, andthen the quick-deflation solenoid valve 60 is closed;

g. when the blood pressure measurement is carried out for the secondtime, repetition of steps starts from step c, or starts from step bperiodically.

The 3-way solenoid valve 20 has a common port communicated with thefirst pressure sensor 30, a normally open port communicated with thecuff during measurement process, and a normally closed port thereof iscommunicated with atmosphere during zeroing process. The 3-way solenoidvalve 20 is driven by a 3-way solenoid valve drive circuit 21 controlledby the primary MCU 100. The primary MCU 100 outputs a high level and alow level for controlling the 3-way valve drive control circuit 21, sothat the solenoid valve 20 is operated in a state wherein the commonport is communicated with the normally open port and not communicatedwith the normally closed port, and a state wherein the common port iscommunicated with the normally closed port and blocked from the normallyopen port.

With reference to FIGS. 1 and 5, during the measurement process of stepf in the non-invasive method, once the state of the overtime oroverpressure occurs, the system immediately closes the air pump 50 andopens the quick-deflation solenoid valve 60. The step f is performed insuch a manner that an independent timing circuit 45 is provided in thesystem, wherein said independent timing circuit 45 is actuated by theprimary MCU 100 so that a control signal OT is output to theoverpressure and overtime control circuit 46 as soon as time is over,and then the circuit 46 immediately opens the quick-deflation solenoidvalve 60 and closes the air pump 50 to release the cuff pressure.

With reference to FIGS. 7 and 8, after the cuff pressure reached thepreset value by inflation process, the data processing during the step dincludes the following steps:

d1: sampling during the deflation process, and thereby obtaining a cuffpressure X and a pressure pulse wave amplitude Y of each sampling point;

d2: taking a cuff pressure X0 and a pressure pulse wave amplitude Y0 ofa first sampling point among the sampling points as initial values, andselecting a pressure step Δ;

d3: selecting at least three adjacent sampling points while sequentiallymoving point-by-point on the basis of the sampling points, and thenperforming data processing as follows for the sampling points until thelast sampling point:

piecewise performing trend term fitting by constructing a multiple-ordercurve with said at least three adjacent sampling points, generating acuff pressure Xm and a pressure pulse wave amplitude Ym of aninterpolation point between two adjacent sampling points of said atleast three adjacent sampling points and then saving Xm and Ym, whereinXm is within a cuff pressure interval of said two adjacent samplingpoints, Xm=X0−mΔ, while each of n and m is a natural number whichincreases by one during such fitting process;

d4: performing smooth processing by taking said pressure pulse waveamplitude of each saved interpolation point as an intermediate value,weighted-averaging or arithmetical-averaging the amplitude of eachinterpolation point with amplitudes of at least two adjacentinterpolation points while moving point-by-point, and thereby obtainingthe smoothed amplitude of each interpolation point and then saving it;and

d5: searching the maximum of pulse wave amplitude among the saved andsmoothed amplitudes, constructing a multiple-order curve with the dataof the point corresponding to the maximum of pulse wave amplitude and atleast one point on either side thereof, and calculating the maximum ofpulse wave amplitude of the multiple-order curve as the extreme value oftrend envelope curve of the oscillating pulse wave, wherein a cuffpressure corresponding to the extreme value is an average pressure.

During step d3 of said algorithm by non-linear fitting to recover thetrend envelope of the oscillating PW, an interpolation value of the PPWamplitude corresponding to the preset cuff pressure X0-mΔ which rangesfrom the cuff pressure value of every first point to that of everysecond point, is generated by piecewise constructing a fitted quadraticcurve with the data of three adjacent sampling points point-by-point.

During step d4 of said algorithm by non-linear fitting to recover thetrend envelope of the oscillating PW, the smooth processing is performedby arithmetically averaging the PW amplitude value of said saved pointand the PW amplitude values of two points on either side of each savedpoint respectively.

During step d5 of said algorithm by non-linear fitting to recover thetrend envelope of the oscillating PW, a quadratic curve is constructedwith the data of the point corresponding to the maximum of PW amplitudevalue for reference, the data of one adjacent point along thepressure-increasing direction and the data of two adjacent point alongthe pressure-decreasing direction by least square procedure, and thenthe extreme value can be obtained from the curve.

During step d5 of said algorithm by non-linear fitting to recover thetrend envelope of the oscillating PW, a quadratic curve is constructedwith the data of the point corresponding to the maximum of PW amplitudefor reference and the data of one adjacent point data to the left sideand right side respectively, and then the extreme value can be obtainedfrom the curve.

A non-invasive electronic apparatus for measuring blood pressureaccording to the present invention mainly comprises the cuff 10, the gaspump 50 connected with the cuff 10, the first pressure sensor 30connected with the cuff 10, the second pressure sensor 40 foroverpressure and overtime protection connected with the cuff 10, thefirst solenoid valve unit for deflation, and the first microprocessor(i.e. the primary MCU) 100. Moreover, the apparatus further comprises asecond solenoid valve which is connected between the cuff 10 and thefirst pressure sensor 30.

In the above-mentioned apparatus of the present invention, the secondsolenoid valve may be a 3-way solenoid valve 20. The first solenoidvalve unit may be composed of one solenoid valve, but preferablycomposed of the quick-deflation solenoid valve 60 and the slow-deflationsolenoid valve 70.

As is shown in FIG. 1, the non-invasive electronic apparatus formeasuring blood pressure according to a preferred embodiment of theabove-mentioned method comprises the cuff 10, the air pump 50, the firstpressure sensor 30, the second pressure sensor 40, the quick-deflationsolenoid valve 60, the slow-deflation solenoid valve 70, the primary MCU100, a display screen 110 and a communication interface 120, wherein a3-way solenoid valve 20 is provided between the cuff 10 and the firstpressure sensor 30. A common port of the valve 20 is communicated withthe first pressure sensor, a normally open port thereof is communicatedwith the cuff during measurement process, and a normally closed portthereof is communicated with atmosphere during zeroing process.

It's also shown in FIG. 1 that, in a preferred embodiment, thequick-deflation solenoid valve 60 is electrically connected with aquick-deflation valve drive circuit 61. An input terminal of saidquick-deflation valve drive circuit 61 is electrically connected withoutput terminals of the primary MCU 100 and the overpressure andovertime control circuit 46. An input terminal of the overpressure andovertime control circuit 46 is electrically connected with the output ofthe independent timing circuit 45.

As shown in FIG. 5, in a preferred embodiment, said independent timingcircuit 45 comprises a second MCU U2 which is preferred to be MSP430micro processor and performs the timing and triggering by means ofsoftware, wherein two I/O pins of said second MCU U2 are electricallyconnected with two I/O pins of the primary MCU 100 to receive a timedelay start instruction, a time delay stop instruction and anadult/infant setting instruction from the primary MCU 100; the secondMCU U2 further has a pin which outputs an overtime signal OT to theoverpressure and overtime control circuit 46.

It is shown that the communication interface 120 is an RS232 interfacein the preferred embodiment, but it may be a USB interface.

As shown in FIGS. 6 and 1, the output of said first pressure sensor 30is electrically connected to a precise amplifier circuit 31. One of theoutputs of the precise amplifier circuit 31 is input to an A/D convertercircuit 35 as a pressure signal CUFFPRESS, while the other output isalso input to the A/D converter circuit 35 as a pulse signal PULSEWAVEafter being amplified by a preamplifier 32 and a postamplifier 33.

The output of the first pressure sensor 30 is connected with a port 2and a port 3 of the precise amplifier 31, while an input pin 4 of thefirst pressure sensor 30 is connected with port 7 of an operationalamplifier U3A. Both a pin 2 and a pin 5 of the first pressure sensor 30in parallel are connected with port 8 of the operational amplifier U3A,wherein a pin 2 of the operational amplifier U3A is grounded, and a pin6 of the operational amplifier U3A is connected with a power source Vccand grounded with AGND via a capacitor C1. In addition, a pin 6 of thefirst pressure sensor 30 is grounded. For amplifier 31, a pin 1 isconnected with a resistor R1 and then connected with a pin 8; a pin 7 isconnected with a power source Vcc and grounded via a capacitor C44; apin 4 is grounded; a pin 5 is connected between resistors R2 and R3.Meanwhile, the other end of the resistor R2 is connected with Vcc andthe other end of R3 is grounded. Moreover, an output pin 6 of theprecise amplifier 31 is divided into two routes, wherein one of routesoutputs the partial voltage to a resistor R12 via series connection of apotentiometer TR1 with a resistor R4 and is further grounded via acapacitor C22 and outputs the pressure signal CuffPress, the other ofroutes is connected with a resistor R5 via a stopping capacitor E1 andis further output to the preamplifier 32 via the resistor R5. At thesame time, programmable gain selection is performed for the preamplifier32, so that different gains are set in different application modes(adult/infant).

In the preferred embodiment, the preamplifier 32 comprises an inputresistor R5, and an additional resistor R6 which is in parallelconnection with the input resistor R5 through a gain control andreference voltage circuit 44 or not in parallel connection with theinput resistor, wherein whether the resistor R6 is in parallelconnection with the input resistor R5 is determined by pins A, B and Cof the gain control and reference voltage circuit 44 under the controlof SETP signal and AN_MODE signal of the primary MCU 100.

The postamplifier 33 also comprises an input resistor R8, and anadditional resistor R9 which is in parallel connected with the inputresistor R8 through the gain control and reference voltage circuit 44 ornot connected with the input resistor R8, wherein whether resistor R9 isin parallel connected with resistor R8 is determined by pins A, B and Cof the gain control and reference voltage circuit 44 under the controlof the SETP signal and the AN_MODE signal of the MCU 100. The magnitudeof the input resistor determines the magnification of the amplifiers,and the primary MCU 100 determines whether the resistors R6 and R9 arein parallel connection with the input resistor R5 and R8 as requiredduring operation.

Said gain control and reference voltage circuit 44 is mainly composed ofdigital circuit 4053 comprising three 2-to-1 bidirectional analogswitches. As to the digital circuit 4053, the control pins A, B, and Care connected with the primary MCU 100, while an output pin X thereof isconnected with an inverting input terminal of the output amplifier 43via a resistor R28, an input pin X1 is connected with reference voltageV1.25 and an pin XO with reference voltage V2.0. Thereby, differentreference voltages lead to different thresholds of the output amplifier43. In addition, pins 7, 8, and 6 of the digital circuit 4053 comprisinganalog switches are grounded with AGND; a pin 9 is for receiving SETPsignal from a port of CPU to perform the connection/disconnection of pin4 with pin 3 or 5; pins 10 and 11 are in parallel connected with eachother for receiving AN_MODE signal from a port of CPU to perform thesynchronous switching of connecting pin 15 with pin 1 or 2 andconnecting pin 14 with pin 13 or 12.

As shown in FIG. 1, FIGS. 6A-6C and FIG. 5, an output of said secondpressure sensor 40 is connected with the voltage follower constituted byan amplifier 41 and the preamplifier constituted by an amplifier 42. Theoutput of the amplifier 42 and an output “X” of the gain control andreference voltage circuit 44 are respectively connected with two inputterminals of the output amplifier 43, while the output terminal of theoutput amplifier 43 outputs as the overpressure signal OP after beingdriven by FET Q7 and the overpressure signal OP is input to theoverpressure and overtime control circuit 46, thereby to ensure thesafety of living body by detecting whether the cuff pressure exceeds thepreset protective pressure point.

The overpressure protection is performed by the followings. A pin 1 ofthe second pressure sensor 40 is connected with a power input VI viaR18. Both a voltage-regulator diode D7 and a capacitor C5 in parallelare grounded AGND, while a pin 3 of the second pressure sensor 40 isalso connected with ground AGND. Furthermore, a pin 4 of the secondpressure sensor 40 is connected with a pin 3 of the amplifier 41,wherein a pin 4 of the amplifier 41 is connected with pin 5 and furtherconnected with pin 8 of the amplifier 42 via the series connection of aresistor R26, a resistor R24 and a potentiometer TR2. In addition, a pin2 of the second pressure sensor 40 is connected with a pin 1 of theamplifier 42, wherein a pin 8 of the amplifier 42 is connected with apin 7 via a resistor R25, said pin 7 is connected with a pin 4 of outputamplifier 43 via a resistor R27. Said pin 4 of the output amplifier 43is connected with a pin 14 of the digital circuit 4053 via a resistorR28 and further connected with reference voltage V1.25 and V2.5 via pin13 or 12 of the digital circuit 4053. Moreover, a pin 5 of the amplifier42 is grounded GND via a resistor R29, while a pin 3 of the outputamplifier 43 is grounded GND and connected with a pin 5 thereof viaresistors R31; pins 3 and 4 of the output amplifier 43 are connectedwith each other via a capacitor C49. Meanwhile, a pin 5 of the outputamplifier 43 is connected with pin 1 of FET Q7, wherein a pin 1 of FETQ7 is also connected with a pin 2 thereof via resistor R35 and groundedAGND, and a pin 3 of FET Q7 is connected with power source Vcc via aresistor R54 and also outputs the overpressure signal OP.

One route of the output of the second pressure sensor 40 is connectedwith the voltage follower constituted by the amplifier 41, and theoutput of the voltage follower is connected with an inverting inputterminal of the amplifier 42. Meanwhile, the other route of output ofthe second pressure sensor 40 is connected with the in-phase inputterminal of the amplifier 42 to perform the pre-amplification of thestatic cuff pressure. Furthermore, the output terminal of suchamplification circuit is connected with the in-phase input terminal ofthe output amplifier 43, while the inverting input terminal of outputamplifier 43 is input with adjustable reference voltage, therebyrealizing the correct state reversion of overpressure protection pointto meet the requirement of setting different overpressure protectionpoints under different application modes.

FIG. 6B shows a circuit for providing reference voltage VREF1, VREF2 andVREF3; and FIG. 6C shows a circuit for providing reference voltage VCC.

As shown in FIG. 5 and FIG. 1, said overpressure and overtime controlcircuit 46 includes the inverters U4-1, U4-2 and NOR gate digitalcircuits U3-1, U3-2. An input terminal of the overpressure and overtimecontrol circuit 46 receives the overtime signal OT output by theindependent timing circuit 45 and the overpressure signal OP output bythe output amplifier 43, while an output terminal of the circuit 46 isconnected with the quick-deflation valve drive circuit 61 andslow-deflation valve drive circuit 71.

The communication interface 120 is an RS232 interface in the preferredembodiment, but it may also be a USB interface in other embodiments.

In the preferred embodiment shown in FIG. 5, an input terminal of saidindependent timing circuit 45 for starting timing is connected with aport P02 of the primary MCU 100. The second MCU U2 shown in the Figureis structured by a single-chip of TI's MSP430, and timing is performedby the system software of MSP430. The software timer is enabled when thesecond MCU U2 detects the signal of enabling the timer, and the softwaretimer is stopped when the second MCU U2 detects the signal of thestopping timer. The time limit of such software timer depends on theapplication mode settings for adult/infant, wherein the time limit is180±1 seconds for adult mode and 90±1 seconds for infant mode.

Certainly, the timer discussed above can also use an analog device ordigital circuit to fulfill the same functions.

In the preferred embodiment of the present invention, I/O port P1.0 ofthe MCU U2 is connected with the input terminal of the overtime controlcircuit 46. The I/O port is maintained at a low level when the system isin standby state rather than in measurement state. However, when thesystem is in measurement state, the I/O port outputs a high level and ismaintained at this level until the measurement process is completed andthen again outputs a low level to maintain the standby state. When oneof the input terminals of the overtime control circuit 46 is at a lowlevel, the timer stays in a state of stopping timing. Only when timingof the timer exceeds the time limit (e.g. 180±1 seconds (for adult) or90±1 seconds (for infant)), does the input terminal output signals toactuate the deflation solenoid valve 70, stop the air pump 50, andnotify the primary MCU 100.

The firmware within the primary MCU 100 is responsible for themeasurement, data processing, result calculation, and communication withthe upper control system during the measurement process. During themeasurement process, the cuff pressure is increased to a preset value byboosting the pressure via the gas path, and then the cuff is deflatedunder the control of the software. During the deflation, the PPWamplitude and corresponding cuff pressure value are obtained for eachsampling point at the same time, wherein the deflation may be instepwise mode or a continuous mode. As shown in FIG. 7, in the conditionthat the cuff pressure is used as the horizontal axis and the PWamplitude is used as the vertical axis, there are discrete data pointsA(X_(A), Y_(A)), B(X_(B), Y_(B)), C(X_(C), Y_(C)) . . . , wherein X_(A),X_(B), X_(C) . . . are sampled values of the cuff pressure withnon-uniform difference. For the sake of convenient calculation and finefitting, during recovering the curve envelope by fitting, non-linearinterpolation is performed in this method of the present invention, sothat a series of data points (X0, Y0), (X1, Y1), (X2, Y2), (X3, Y3) withuniform pressure difference which represent the curve envelope, in whichX1−X0=X2−X1=X3−X2= . . . =Δ, and then the data points are processed bycalculation.

As shown in FIG. 8, the detailed processing flow comprises the followingsteps:

a. taking cuff pressure of the first sampling point (X0, Y0) as theinitial value, and selecting a pressure step Δ which is used later toproduce data for an interpolation point (X_(m), Y_(m)) by subsequenttrend term fitting with each sampling point (X_(n), Y_(n)) as theintermediate value, where n, m are natural number, and X_(m)=X0−mΔ;

b. on the basis of said sampling points, selecting a set of at least 3adjacent sampling points by sequentially moving the sampling pointspoint-by-point, and then performing piecewise trend term fitting byconstructing a multiple-order curve with said at least 3 points; duringthe cuff pressure in the range between cuff pressure of the first pointand cuff pressure of the second point, the PPW amplitude Ym ofinterpolation points corresponding to each preset cuff pressureinterpolation X0-mΔ within a range between the cuff pressure of thefirst point and the cuff pressure of the second point are generated andsaved in turn; and n, m increase by one during this process;

c. smooth processing is carried out by taking said PW amplitude of eachsaved interpolation point which has been saved as the intermediatevalue: said amplitude of each point is moved point-by-point so as to beweighted-averaged or arithmetical-averaged with the amplitude of atleast two adjacent points; then the flattened amplitude of the point isobtained and saved;

d. searching the maximum of PW amplitude in the saved and smoothedamplitudes, taking such position for reference, selecting at least onepoint on either side thereof respectively to construct a multiple-ordercurve with the selected points, calculating the maximum value of themultiple-order curve, taking the maximum value as the extreme value ofthe trend envelope curve of oscillating PW, and determining thecorresponding cuff pressure as average pressure.

In the above steps, the pressure step Δ in step a can be selected fromthe pressure difference range of 3-5 mmHg depending on the living body.The quadratic curve of in step b is fitted by three points, and can beexpressed as Y=a_(n)X²+b_(n)X+c_(n), where:

Y _(n) Y(X _(n)), Y _(n+1) =Y(X _(n+1)), Y _(n−1) =Y(X _(n−1))

Thereby a_(n), b_(n), and c_(n) can be determined, and data Ym atpressure of X0−mΔ≦Xn can be further calculated. If the system hassufficient resource and operation speed, a multiple-order curve can beconstructed with at least 3 points and non-linear interpolation isperformed.

Instead of interpolating between the first two sampling points of eachsegment as shown in the example, interpolation can be performed betweenthe last two sampling points; in the case of trend term fitting with allthe sampling points (Xn, Yn) as the intermediate value, since thesampling points are generally sufficient, it is allowed to give up theinterpolation between the last two sampling points or the first twosampling points.

During the smooth filter processing in step c, the method of movingweight average of adjacent points is used, e.g. five points, and inpractice, weight average of 3 points or 4 points can also be used. Saidweight average can also be simplified into arithmetic average.

To improve the data accuracy, the above step d can be further processed,as shown in FIG. 7: according to the inquired maximum position, oneadjacent data point is selected along the pressure increasing directionand two adjacent data points along the pressure decreasing direction, sothat the side with sharper trend contains more data points to ensure thetrend weight of the rising edge; then on the basis of 4 data pointsmentioned above, a quadratic curve is constructed by the least squareprocedure, and the peak of such curve is confirmed to be the extremevalue of trend envelope of the PW amplitude, which corresponds with theaverage pressure; based on the extreme value of the amplitude, thecorresponding amplitude of systolic pressure and diastolic pressure canbe further calculated, and thereby deriving the systolic pressure andthe diastolic pressure from the envelope.

During the implementation of the present invention, the data acquisitionand pre-processing program module of the system software will also carryout the identification of reference wave and the calculation andestimation of the amplitude for PW. Only when the normal trend pulseoccurs, the subsequent pulse fitting and interpolation is carried out,and further calculation of the blood pressure is performed. When normaltrend pulse is not found, the module continues finding PW or reportabnormality and produces corresponding error information, which is notdescribed here since it is beyond the scope of the present invention.

It has been proved that the present invention optimizes the connectionstructure of the gas path, and that automatic and accurate “zeropressure point” calibration of the cuff pressure is performed withoutthe influence of the residual pressure in the gas path, which improvesthe accuracy of the measurement of cuff pressure.

Furthermore, the independent time-limiting timing function can beperformed by means of a set of independent timing circuit, which canreally perform the independent timing in the module level and improvethe safety during measurement of blood pressure.

In the present invention, the trend envelope of oscillating PW isrecovered by non-linear fitting, which can obtain both the maximum valueof the PW and the average pressure. The obtained average pressure isproved to show higher degree of agreement with the real situation inclinic. In particular, the data obtained by stepwise deflation can beprocessed effectively, which shortens the measurement process and helpsto improve the safety.

While specific embodiments and applications of the present inventionhave been illustrated and described, it is to be understood that theinvention is not limited to the precise configuration and componentsdisclosed herein. Various modifications, changes, and variationsapparent to those of skill in the art may be made in the arrangement,operation, and details of the methods and systems of the presentinvention disclosed herein without departing from the spirit and scopeof the present invention.

1. A non-invasive electronic apparatus for measuring blood pressure,which comprises a cuff, a gas pump connected with the cuff, a firstpressure sensor connected with the cuff, a second pressure sensorconnected with the cuff for overpressure and overtime protection, afirst solenoid valve unit for deflation, and a first microprocessor,wherein the apparatus further comprises a second solenoid valve which isconnected between the cuff and the first pressure sensor.
 2. Thenon-invasive electronic apparatus for measuring blood pressure accordingto claim 1, wherein the second solenoid valve is a 3-way solenoid valve,wherein a common port of the valve is communicated with the firstpressure sensor, a normally open port thereof is communicated with thecuff during measurement process, and a normally closed port thereof iscommunicated with atmosphere during zeroing process.
 3. The non-invasiveelectronic apparatus for measuring blood pressure according to claim 1,further comprising an independent timing circuit with timing function,wherein an output terminal of the circuit outputs an overtime signal toan overpressure and overtime control circuit for overpressure andovertime protection, while an input terminal thereof is connected withthe first microprocessor for actuating the independent timing circuit.4. The non-invasive electronic apparatus for measuring blood pressureaccording to claim 3, wherein the independent timing circuit includes asecond microprocessor having a timing and triggering function bysoftware, wherein the second microprocessor has two I/O pins connectedwith two I/O pins of the first microprocessor, for receiving a timedelay start instruction and a time delay stop instruction and anadult/infant setting instruction from the first microprocessor; and thesecond microprocessor further has another pin for outputting an overtimesignal to the overpressure and overtime control circuit.
 5. Thenon-invasive electronic apparatus for measuring blood pressure accordingto claim 3, wherein the first solenoid valve unit comprises aquick-deflation solenoid valve and a slow-deflation solenoid valve whichare connected with the cuff, wherein the quick-deflation solenoid valveis connected with a quick-valve driving circuit and the slow-deflationsolenoid valve is connected with a slow-valve driving circuit, whileeach of the quick-valve driving circuit and the slow-valve drivingcircuit is connected with the first microprocessor and the overpressureand overtime control circuit.
 6. The non-invasive electronic apparatusfor measuring blood pressure according to claim 3, further comprising acombined precise amplification circuit including a voltage follower, apreamplifier and an output amplifier which are connected in series,wherein the combined precise amplification circuit has an input terminalconnected with an output terminal of the second pressure sensor and hasan output terminal for outputting an overpressure signal to an inputterminal of the overpressure and overtime control circuit.
 7. Thenon-invasive electronic apparatus for measuring blood pressure accordingto claim 6, further comprising a gain control and reference voltagecircuit which has an output terminal connected with an input terminal ofthe output amplifier.
 8. The non-invasive electronic apparatus formeasuring blood pressure according to claim 7, wherein the gain controland reference voltage circuit includes a digital circuit having three2-to-1 bidirectional analog switches which have an output pin Xconnected with an inverting input terminal of the output amplifier, aninput pin X1 connected with a reference voltage V1.25, and a pin X0connected with a reference voltage V2.0.
 9. The non-invasive electronicapparatus for measuring blood pressure according to claim 1, furthercomprising a precise amplifier having an input terminal connected withan output of the first pressure sensor, wherein the precise amplifieroutputs both a pulse signal amplified by a two-stage amplificationcircuit and a pressure signal to an A/D converter circuit.
 10. Thenon-invasive electronic apparatus for measuring blood pressure accordingto claim 9, further comprising a gain control and reference voltagecircuit which has an output terminal connected with the two-stageamplification circuit; the two-stage amplification circuit comprises apreamplifier and a postamplifier which are connected in series, whereinan input terminal of the preamplifier or the postamplifier is connectedwith a first resistor, while a second resistor is in parallel connectedwith or not connected with the first resistor via the gain control andreference voltage circuit, which is determined by pins A, B and C of thegain control and reference voltage circuit controlled by SETP andAN_MODE signals from the first microprocessor.